Ammunition cartridge

ABSTRACT

Ammunition cartridge comprising a rigid casing including a tubular sleeve and a base closing an end of the casing, a projectile mounted at another end of the casing, a propellant charge contained inside the casing, and an ignition device. The projectile comprises a solid material body having a volume V1 extending between a tip to a trailing end, wherein the projectile further comprises a cavity that extends into the body from the trailing end, a volume V2 of the cavity being at least fifteen percent (15%) of a combined volume V1+V2 of the projectile solid material and cavity: V2&gt;0.15×(V1+V2).

FIELD OF THE INVENTION

This invention relates to an ammunition cartridge for rifles andfirearms.

BACKGROUND OF THE INVENTION

Conventional ammunition cartridges for firearms and guns of varioussizes and purposes typically comprise a deep drawn brass or steel casingcontaining a propellant charge in the form of powder or granules of acombustible substance, and a projectile assembled in a gripping fit atan open tubular sleeve end of the casing. Most projectiles are massive,cylindrical objects with an aerodynamic tip at the front and a flaredshape with a flat base at the rear. The latter is usually mounted insidethe cartridge casing whereas the aerodynamical tip is outside thecartridge casing.

The propellant's combustion and its release of a large quantity of gaspushes the projectile through the barrel providing it with substantialkinetic energy. The relationship between combustion, gas pressure andprojectile velocity may be modelled computationally, as per se known andillustrated in FIG. 7 . This per se known model shows that combustionoccurs approximately in the first third of the barrel, that maximumpressure occurs approximately in the first tenth of the barrel and thatacceleration of the projectile occurs substantially in the first half ofthe barrel. These relations depend principally on the weight of theprojectile, the quantity of propellant, its specific combustion energyand the initial volume in which the combustion starts. The combustionvolume increases as the projectile moves into the barrel but is has beenshown by model calculations, as well as experimental measurements, thatthe maximum pressure produced by the combustion is very much dependenton the initial combustion volume, i.e. the internal volume of thecartridge before ignition.

Considering that the pressure tolerance of most weapons is set at about4′000 bars and that the cartridge internal volume is also specified bythe weapons geometry, the propellant's specific energy and its weighthave long been optimized in order to provide the largest velocity forevery specific projectile mass. Any change in the propellant's specificenergy or its quantity leads to an unacceptable overpressure.

The pressure generated by combustion of the propellant substance mustnot exceed a certain level in order to prevent damage to the weapon. Inmany conventional weapons the pressure generated by the combustingpropellant should not exceed around 4000 bars. This limits thepropulsion force that the propellant charge can impart.

Another major concern with modern ammunition is related to the range ofthe projectile. Increasing the projectile range is a high requirement asthis sets the distance at which the enemy can be held. High ranges pausehowever serious problems when it comes to training and security ofshooting ranges. In such cases it is highly desirable that theprojectile's flight is limited to a much shorter distance than the oneit can cover. Desired training projectiles are expected to lose theirstability at a certain point of their trajectory and consequentlyinterrupt their flight.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the invention to provide anammunition cartridge with to improved performance, in particular thatallows to generate a high and well controlled acceleration of theprojectile without exceeding the chamber pressure tolerance, and that issafe to use.

It is another object of the invention to provide an ammunition cartridgethat is suitable for training purposes by limiting voluntarily the rangeof the projectile.

It is advantageous to provide an ammunition cartridge that is economicalto manufacture in large quantities.

It is advantageous to provide an ammunition cartridge that is light,compact, and uses less materials for a given performance.

It is advantageous to provide improved ammunition cartridges that can beused in existing weapons.

Objects of this invention have been achieved by providing the ammunitioncartridge according to claim 1.

Objects of this invention have been achieved by providing the ammunitioncartridge according to claim 24.

Objects of this invention have been achieved by providing the ammunitioncartridge according to claim 16.

Dependent claims recite various advantageous features or variants.

Disclosed herein, is an ammunition cartridge comprising a rigid casingincluding a tubular sleeve and a base closing an end of the casing, aprojectile mounted at another end of the casing, a propellant chargecontained inside the casing, and an ignition device. The projectilecomprises a solid material body having a volume V1 extending between atip to a trailing end wherein the projectile further comprises a cavitythat extends into the body from the trailing end, a volume V2 of thecavity being at least fifteen percent (15%) of a combined volume V1+V2of the projectile solid material and cavity: V2>0.15×(V1+V2), and thevolume V2 of the cavity is less than forty percent (40%) of the combinedvolume of the projectile solid material and cavity: V2<0.4×(V1+V2).

According to an aspect of the invention, the casing is made of at leasttwo parts including a base and a tubular sleeve that are assembledtogether, preferably welded together. The tubular sleeve mayadvantageously be made of stainless steel, and preferably the base isalso made of to stainless steel.

According to an aspect of the invention, the present invention isparticularly advantageous for ammunition having a length of the casingrelative to an outer maximum diameter of the casing (casing tubularsleeve) in a range of 4.5 to 7 and a depth of the cavity from thetrailing end is preferably in a range of 1 to 3 calibers.

In an advantageous embodiment, the volume V2 of the cavity is at leasttwenty percent (20%) of the combined volume V1+V2 of the projectilesolid material and cavity: V2>0.20×(V1+V2).

In an advantageous embodiment, the volume V2 of the cavity is less thanthirty percent (30%) of the combined volume V1+V2 of the projectilesolid material and cavity: V2<0.30×(V1+V2).

In an advantageous embodiment, the depth of the cavity from the trailingend is at most 2.5 calibers.

In an advantageous embodiment, the depth of the cavity from the trailingend is at least 1.5 calibers.

In an advantageous embodiment, the propellant fills an inside of thecasing and extends at least partially into the cavity of the projectile.The propellant may be in the form of loose granules or powder, or in asolid pre-form.

In an advantageous embodiment, the tubular sleeve is made of a sheet ofmetal rolled into a tube and welded along a seam.

In a variant, the tubular sleeve is made of an extruded tube of metal.

According to yet another aspect of the invention, the projectilecomprises a flight destabilizing device comprising a consumable materialmounted in the cavity and configured to deplete as the projectile fliesthus offsetting a centre of gravity (CG) of the projectile from a centrelongitudinal axis (A) of the projectile.

In an embodiment, the consumable material comprises or consists of apyrotechnically active material.

In an embodiment, the consumable material is mounted in a recess in anend wall of the cavity, to the recess being asymmetrically disposed withrespect to the longitudinal centre axis (A).

In an embodiment, the consumable material comprises an additional layerarranged around the longitudinal centre axis in such a manner that thecentre of gravity (CG) of the projectile remains on its centrelongitudinal axis even as the additional layer is thinned as it is beingconsumed.

In an embodiment, the projectile comprises a flight destabilizing devicemounted in the cavity, comprising a consumable material and an explosivecharge, the consumable material configured to deplete as the projectileflies until such time where it ignites the explosive charge todestabilize the projectile.

In an embodiment, the projectile comprises a flight destabilizing devicemounted in the cavity, comprising an explosive charge, ignited by anelectric ignition device comprising a conductive coil configured toinduce an electric current in the presence of a magnetic field todetonate said explosive charge.

Further objects and advantageous aspects and embodiments of theinvention will be apparent from the claims, and from the followingdetailed description and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings, which by way of example illustrate embodiments of the presentinvention and in which:

FIG. 1 is a schematic cross-sectional view of an ammunition cartridgeaccording to a first embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of an ammunition cartridgesimilar to FIG. 1 a but of a variant;

FIGS. 2 a to 2 c illustrate steps of assembly of the cartridge of FIG. 2;

FIG. 3 is a schematic cross-sectional view of an ammunition cartridgeaccording to a second embodiment of the invention;

FIG. 3 a is a cross-sectional view of a stainless steel two-part casingfor the cartridge of FIG. 3 ;

FIGS. 3 b and 3 c are similar to FIG. 3 a with projectiles mounted inthe casing with different sized cavities;

FIGS. 4 a-4 c are graphical representations of the pressure, velocityand combustion profiles of a simulated combustion process with aprojectile having a cylindrical cavity of 25% of its nominal volumeaccording to an embodiment of the invention;

FIGS. 5 a-5 b are graphical representations of the pressure, velocityand combustion profiles of a simulated combustion process with aprojectile having a cylindrical cavity of 31% of its nominal to volumeaccording to an embodiment of the invention;

FIGS. 6 a-6 b are graphical representations of the pressure, velocityand combustion profiles of a simulated combustion process with a twopart stainless steel casing and a projectile having a cylindrical cavityof 25% (FIGS. 6 a ) and 31% (FIG. 6 b ) of its nominal volume accordingto an embodiment of the invention;

FIG. 7 is a graphical representation of the pressure, velocity andcombustion profiles of a simulated combustion process with aconventional projectile;

FIG. 8 is a schematic representation of projectile halves with differentcavity volumes (depths) to illustrate the position of the centre ofgravity (CG) and centre of aerodynamic pressure (CP);

FIG. 9 a illustrates a plot of kinetic energy change versus an increasein cartridge internal volume according to an embodiment of the inventioncompared to conventional ammunition cartridges with brass casings andfor different propellant filling levels;

FIG. 9 b illustrates a plot of maximum pressure achieved duringcombustion versus an increase in cartridge internal volume according toan embodiment of the invention compared to conventional ammunitioncartridges with brass casings and for different propellant fillinglevels;

FIG. 9 c FIG. 9 a illustrates a plot of velocity change versus anincrease in cartridge internal volume according to an embodiment of theinvention compared to conventional ammunition cartridges with brasscasings and for different propellant filling levels;

FIG. 9 d illustrates a plot of change in mass of the ammunitioncartridge versus an increase in cartridge internal volume according toan embodiment of the invention compared to conventional ammunitioncartridges with brass casings;

FIGS. 10 a-10 d are schematic cross-sectional views of a projectile withdestabilizing device of an ammunition cartridge according to anembodiment of the invention, illustrating functioning of thedestabilizing device to limit range of the projectile;

FIG. 11 is a schematic cross-sectional view of a projectile withdestabilizing device of an ammunition cartridge according to anotherembodiment of the invention;

FIG. 12 a is a schematic cross-sectional view of a projectile withdestabilizing device of an ammunition cartridge according to anotherembodiment of the invention.

FIG. 12 b is a schematic view of a portion of an electric field fencefor triggering the destabilizing device of FIG. 12 a

FIG. 13 is an illustration of various conventional common calibercartridges, showing the length of the cartridges, all these cartridgesprovided with conventional brass casings.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to FIG. 1 , an ammunition cartridge comprises a casing 4, aprojectile 6, an ignition to device 8, and a propellant charge 10. Theprojectile 6 may have various materials and geometric properties thatare per se known in the field of ammunition cartridges and has adiameter defining a caliber configured for a barrel of a weapon. Thecasing diameter D and length L are dependent on the loading chamber ofthe weapon it is intended for use with. The ammunition cartridge outershape and dimensions may advantageously be configured to conform to astandard size for use with existing firearms and rifles, in replacementof existing ammunition cartridges.

The casing 4 generally has a cylindrically shaped tubular sleeve 16closed at one end by a base 14 housing an ignition device 8, and at theother end of the casing the projectile 6 is fitted. The projectilereceiving end, as is well-known in the art, comprises a neck portion 24connected via a tapered portion to a major portion 25 of the tubularsleeve portion containing the propellant charge 10, the neck portion 24having a smaller diameter than the major portion 25. The outer shape ofthe base may have various configurations depending on the weapon withwhich it is intended to be used, and may for instance typically comprisea rim 27 and annular groove 29 that serve to eject the casing from thefiring chamber of the weapon as is per se well-known in the art.

In a first embodiment, the casing 4 may be made of a single piece part,namely formed from a single piece of material such as a conventionalbrass ammunition casing, for instance as illustrated in FIGS. 1 and 2 .

The present invention is in particular adapted for long ammunition usedfor rifles, for instance ammunition types as illustrated in FIG. 13 .The ratio L/D of length L to maximum diameter D of the casing for suchammunition is in a range of 4.5 to 7 (four and a half to seven),preferably in a range of 5 to 7 (five to seven).

According to an aspect of the invention, the casing may be assembledfrom two or more parts, as illustrated in FIG. 3 , with at least acylindrical body or sleeve 16 and a base 14, that are assembled togetherby welding, soldering, or crimping. The latter embodiment allowsassembly of the propellant charge 10 into the casing tubular sleeve fromthe base end 31 before assembly of the base 14 to the tubular sleeve 16,or in a conventional manner from the open neck end 33 once themulti-part casing is assembled. The casing is preferably made of steel,whereby the tubular sleeve 16 may be made from sheet metal, rolled intoa tube and welded along an axial seam. The tubular sleeve may also beextruded. The tubular sleeve is preferably welded to the stainless steelbase 14.

The propellant charge 10 may be in the form of powder or granules as perse known in the art. The embodiment illustrated in FIGS. 2 a to 2 ccomprises a propellant charge in the form of powder or granules.

In another embodiment, the propellant charge is bound in a preform thatforms a solid body insertable into the tubular sleeve 16 of the casing4. The preform may comprise a combustible substance bound together witha binding material. The embodiment illustrated in FIG. 3 comprises apropellant charge bound in a solid preform.

In an embodiment, as illustrated in FIGS. 1 and 2 , the ignition device8 is fully mounted in the base 14 and ignites the propellant 10 at theend distal from the projectile 6, in a manner widely known inconventional ammunition cartridges.

In another embodiment, the ignition device 8 is configured to ignite thepropellant 10 at a position distal from the base 14 and proximate theprojectile 6. Ignition of the propellant charge 10 at a positionproximate the projectile 6 may be achieved in various manners.

In an embodiment as schematically illustrated in FIG. 3 , the ignitiondevice comprises a transmission pin 35 slidably mounted in a guidechannel 37 extending from the base 14 to a position proximate theprojectile 6. A first ignition charge 39 a positioned in the base 14 ofthe cartridge may be ignited by a firing pin or hammer of the weapondeforming the ignition cap, similar to a conventional ammunitioncartridge ignition process, whereby in this variant the guide channel 37channels the pressure of expanding gas generated by combustion of theignition charge 39 a to propel the transmission pin 35 towards a basewall of the projectile on which a second ignition charge 39 b ispositioned and is ignited by impact of the transmission pinthereagainst. Combustion of the second ignition charge ignites theleading end 41 of the propellant 10 facing and proximate the projectile6.

The projectile 6 extends from a pointed tip 18 to a trailing end 20. Acentre portion of the projectile comprises a cylindrical shape that iscoupled in a tight friction fit to the neck portion 24 of the casing.The outer diameter of the trailing end is less than the centre bodyportion 22, as per se known, inter alia to facilitate insertion assemblyof the projectile into the casing 4.

According to an aspect of the invention, the projectile 6 comprises acavity 12 that extends into the body of the projectile from the trailingend 20, the volume of the cavity 12 being at least fifteen percent(15%), preferably at least twenty percent (20%), for instance aroundtwenty five to percent (25%), but less than fifty percent (50%), of thecombined volume of the projectile solid material (V1) and cavity (V2):

V2>0.15×(V1+V2), preferably V2>0.2×(V1+V2)

V2<0.5×(V1+V2), preferably V2<0.4×(V1+V2)

The combined volume of the projectile solid material (V1) and cavity(V2) is also referred to herein as the “nominal” volume of theprojectile (i.e. the volume of a conventional projectile withoutcavity), and the nominal mass of the projectile corresponds to the massof the nominal volume of projectile material.

Advantageously, the cavity 12 formed into the body of the projectilewith the aforementioned dimensions increases the initial combustionvolume and thus allows increasing the propellant quantity and itsreleased energy without exceeding the maximum pressure tolerance (set atabout 4′000 bars). The increase in combustion volume also allowsproviding a propellant with a higher specific energy. More kineticenergy can thus be transferred to the projectile.

Another advantage of the cavity as described above is the shift of thecentre of gravity CG of the projectile towards the centre of pressure CPacting on the projectile as it displaces in air, thus providing greaterstability.

Simulations and experiments have shown that the maximal pressuregenerated by the combustion of the propellant is very much dependant onthe size of the initial volume, i.e. the volume in which the propellantstarts its gas generating combustion.

FIGS. 4 a to 6 b illustrate the benefits of the present invention in theexemplary cases of projectiles with cavities forming 25% and 31% of thenominal volume of the projectile.

In FIG. 4 a , the simulation model, which refers to a projectile mass of75% of the nominal projectile mass, shows a substantial maximum pressuredrop to about 2′700 bars down from about 3′500 bars. The cavity portionof the projectile offers however an additional volume of about 8% of theinternal casing volume. One can consequently increase the quantity ofpropellant by 8% and take advantage of the fact that the initialcombustion volume has also increased by 8%. The resulting maximumpressure remains however below the 4′000 bars weapon tolerance as shownin FIG. 4 b . Room is left for an increase in the propellant's specificenergy by about 15% with an increase of the maximum pressure to about4′000 bars as shown in FIG. 4 c . It is important to note that theprojectile velocity has increased by about 24% and to its kinetic energyhas increased by about 15%.

Similarly, FIGS. 5 a and 5 b depict the inner ballistic behavior of a31% hollowed-out projectile. With an increase of 10% of the availablevolume and 4′000 bar matching specific energy increase of 18%, theprojectile velocity increases by 30% and its kinetic energy by some 17%.

If thin walled Stainless-Steel casings, such as shown in FIG. 3 , areused instead of standard brass casings an additional 12% of internalvolume may be made available. A 25% hollowed-out projectile would offera velocity increase of 27% and a kinetic energy increase of some 21%(see FIG. 6 a ) whereas a 31% hollowed-out projectile would provide avelocity increase of 32% and a kinetic energy increase of 21% (see FIG.6 b ). A casing assembled from two or more parts as for instanceillustrated in FIG. 3 , may advantageously comprise a tubular sleeve 16made of stainless steel that is thinner than conventional brass casings.

Conventional brass casings are made of a single piece brass part formedin a deep drawing process that leads to a tapered thickness side walland a rounded internal surface on the base.

By providing a two part stainless steel casing, the internal volume ofthe cartridge is increased by having a thinner base and thinner constantthickness walls of the tubular sleeve.

The internal volume gain, relative to the outer volume of the casing(which is defined by the caliber and chamber dimensions of the rifle andis thus invariable for a given weapon), by replacing a brass casing witha two part stainless steel casing, is in the range of up to 10% to 15%,and for most ammunition cartridges in a range of 11% to 13%, inparticular about 12% as mentioned above.

This internal volume gain adds to the volume of the cavity 12 in theprojectile 6 to achieve, for a given maximum allowable pressure duringcombustion of the propellant, a higher velocity projectile with higherkinetic energy than achievable with a conventional ammunition cartridge.

This increased performance is not due only to an increase in the amountof propellant, but importantly, also a reduction of the peak pressuredue to the increased initial volume. At the beginning of combustion ofthe propellant, the increased internal volume in the casing andprojectile reduces compression of the combusting gas in the very initialphase of ignition as the projectile exits the casing.

The inner ballistics values mentioned in FIGS. 4 a to 6 b have beenderived from a mathematical model that has been validated in part withpressure/velocity measurements in reference weapons. Although thedepicted values are simulations and may thus vary to some degree fromexperimental values, their tendencies are good indicators of theperformance improvements that can be achieved.

Referring to FIGS. 9 a to 9 c , plots showing the performance increasein an ammunition cartridge according to embodiments of the invention areillustrated. In these figures, a two-part stainless steel casingreplacing a conventional brass casing for a given caliber and type ofammunition is illustrated. Various known conventional ammunition typesfor rifles illustrated in FIG. 13 for instance would have values closeto the values illustrated in FIGS. 9 a to 9 c assuming a replacement ofthe brass casing with a stainless steel two-part casing according toembodiments of the invention and by replacing the projectile with ahollow projectile. The depth of the cavity measured as a function of thecaliber is also indicated in rounded-up values because they aredependent on the diameter of the cavity. An important consideration inthe increase in performance is the increased velocity illustrated inFIG. 9 c . The greater the cavity in the projectile, the lower the mass,however the larger the internal volume and amount of propellant that canbe used. The increase in velocity with a lower mass means that theprojectile has a flatter flight profile and longer range, which alsoleads to increased shooting accuracy. This performance increase is ofparticular benefit for ammunition of types illustrated in FIG. 13 usedfor long barrel weapons (such as rifles and machine guns), with a ratioL/D of casing length L divided by casing diameter D in the range of 4.5to 7, in particular 5 to 7.

The increase in internal volume compared to a conventional cartridgeinternal volume is indicated and also the increase in internal volumerelative to the external volume which is a defined value that depends onthe type of ammunition. In effect, the external volume forms a referencevolume because it depends on the chamber size and the caliber that areconstant or fixed values for a given weapon. Thus, whether producing atwo-part stainless steel cartridge with hollow projectile or aconventional cartridge, the external shape and dimensions of theammunition cartridge should be the same since they are defined by theweapon characteristics.

In these plots, the starting point is at 112% of increased internalvolume over a conventional cartridge due to the casing alone, asmentioned above. The relative increase in internal volume measured withrespect to the external volume is also indicated for reference, as 107%.The increase in internal volume above 112% relative to a conventionalcartridge is due to the cavity 12 in the hollow projectile 6 causing anincrease in the internal volume from 112% to 130% (107% to 117% whenmeasured relative to the invariable external volume). The contributionof the cavity 12 in increasing the internal volume ranges thus from 0%to 18% on these plots.

As can be seen in FIGS. 9 b and 9 c , the increased internal volumecompared to a conventional brass cartridge allows a greater amount ofpropellant charge which can vary from 110% to about 150% withoutexceeding a given peak pressure, here set at 3500 bars, as shown in FIG.9 b.

Referring to FIG. 9 a , the increase in kinetic energy of the projectileis shown, here also as a function of the amount of propellant comparedto a conventional casing as a function of the amount of hollowing partof the projectile. Since the hollowing out of the projectile 6 reducesits mass, for a given amount of propellant, the kinetic energy reduces.However, since there is a greater amount of propellant the kineticenergy may be increased up to about a 26% increase in the internalvolume compared to a conventional internal volume of a conventionalcartridge (or if measured with respect to the external volume about a20% increase of internal volume relative to the external volume of aconventional cartridge).

The isobar line Li for 3500 bars in FIG. 9 a is represented and showsthat the optimum performance in this example is achieved between 114%and 122%, in particular between 116% and 120% relative to the internalvolume of a conventional casing (or with respect to the external volumebetween 108% and 112%, in particular between 109% and 111%). The optimumperformance in this example is at 18% increase in internal volume. Theprojectile in this example for optimum performance has a cavity volumeV2 between 8% and 38%, preferably between 15% and 30% relative to thevolume of a full projectile V1+V2. At the optimum, the cavity volume V2is about 23% of the volume of a full projectile V1+V2, i.e.V2/(V1+V2)=23%.

It may be noted in FIG. 9 a that the increase in kinetic energy that maybe achieved is 20% compared to a conventional ammunition cartridge andis thus a significant improvement. In addition to the increasedperformance, the ammunition cartridges according to embodiments of theinvention also have a reduced weight in view of the reduced volume ofmetal (casing and projectile) which is not offset by the increasedamount of propellant which has a much lower density. Thus, lighterammunition can be provided yet with higher performance.

FIG. 9 c illustrates the increased velocity of the projectile obtainedby different amounts of propellant charge and increasing internal volumecompared to a conventional ammunition cartridge. The increase invelocity compensates for the decrease in mass for maintaining a highkinetic energy discussed in relation to the plot of FIG. 9 a.

Referring to FIG. 9 d , the reduction in weight of the completecartridge as a function of the increase in internal volume is shown,whereby in the region of optimum performance, namely about 18% increaseinternal volume relative to the internal volume of a conventional casing(or to 10% increase in volume relative to the external volume of aconventional casing) there is a weight reduction of about 25%.

In addition to the aforementioned advantages, hollowed-out projectilesoffer an improved stability because the distance between their centre ofgravity (CG) and the centre of aerodynamic pressure (CP) issubstantially smaller than in the case of a not hollowed-out projectile.The leverage of the aerodynamic pressure diminishes and the torque thatcan affect the projectile's flight is also reduced. The nutation angleof projectile is consequently reduced which means that the projectile'salignment remains closer to the flight trajectory.

In FIG. 8 projectiles with different cavity lengths are presented interms of Calibers. A Caliber is usually defined as the diameter of thebore of a gun or the maximum diameter of the corresponding projectile.Using calibers as unit of measurement allows making descriptionsindependent of specific projectiles. FIG. 8 shows how the centre ofgravity (CG) moves towards the tip of the projectile, and towards thecentre of aerodynamic pressure (CP) as the cavity length is increased. Amaximum reduction of the CG-CP distance of about 25% is reached with acavity length of about two Calibers. For larger values the centre ofgravity regresses away from the tip and in the case of projectiles wherethe centre portion is substantially fully hollowed out, the centre ofgravity (CG) does not move significantly and there is little reductionin the CG-CP distance.

Thus, there is a significant advantage in having a projectile that has acavity 12 with a volume V2 between 15% and 30% of the total projectilevolume V1+V2 for both the increased performance and reduced weight aswell as maintaining the stability of the projectile as discussed abovein relation to FIG. 8 .

FIGS. 2 a to 2 c illustrate assembly of a cartridge 4 with a propellantformed of granular powder 10 and a projectile 6 according to anembodiment of the invention. A larger than conventional quantity ofpropellant is filled in the casing to take into account the additionalvolume available inside the cavity 12 of the projectile 6. In theinitial assembly step shown in FIG. 2 a the casing is filled withpropellant up to a portion of the casing neck portion 24. When theprojectile 6 is inserted in the casing neck portion 24, as shown in FIG.2 b , granular propellant will flow into the projectile cavity 12 in afluid like behavior. This process can continue with or without a littleshaking of the cartridge until the projectile is normally inserted asshown in FIG. 2 c . The resulting cartridge has a larger quantity ofpropellant than a conventional cartridge with a non-hollowed projectile,and offers also a larger initial combustion volume.

For embodiments comprising a pre-formed solid propellant charge, forinstance as illustrated in FIG. 3 , a leading portion 43 of thepropellant charge may be shaped to insert partially (as shown) or fullyinto the cavity 12 of the projectile.

In a preferred embodiment the cavity may have a cylindrical orsubstantially cylindrical shape, however in other embodiments within thescope of the invention, the cavity may have other axisymmetric shapessuch as conical, parabolic or elliptical, or may have non-axisymetricshapes such as a cavity with a polygonal cross-section. In yet otherembodiments the cavity may comprise a plurality of cavities extendinginto the solid material body of the projectile. The term “cavity” asused herein shall thus, for simplicity, refer to one cavity if there isa single cavity, or to the combined plurality of cavities, if there aretwo or more cavities.

Projectiles with a cavity of 15% nominal volume or more extending intothe trailing end represent an interesting ammunition improvement becausethey are fully compatible with existing weapons. For such weapons, thespecific energy of the propellant would usually be increased in order tomatch the 4′000 bars tolerance. For new weapons, one could howevercontemplate other inner-ballistics variables and select them in order toachieve sufficient kinetic energy with a maximum pressure as low aspossible. Reducing maximum pressure can relax the pressure tolerance andallow lighter weapons.

It may be noted that it is known to hollow-out the material of aprojectile for flight tracing purposes, whereby the hollowed-out portionis filled with a pyrotechnical agent that evaporates after theprojectile leaves the barrel to show the projectile's flight path. Asthe projectile remains filled until the projectile leaves the barrel,the removed mass of projectile material cannot contribute to theavailable initial volume.

Another concern with high speed, long range ammunition is related withthe ability to train safely, in other words to find ranges long enoughto avoid any casualty. As such ranges become difficult to find, there isa growing need for exercise ammunition with artificially limited ranges.The desire is to allow the external ballistics to deploy normally untila specified training limit distance where the projectile flight shouldbecome unstable and substantially reduce the trajectory of theprojectile.

Another aspect of the present invention is thus to provide a means ofdestabilizing the projectile flight after a certain flight time.

In an embodiment illustrated in FIGS. 10 a to 10 d , the end-wall of thecavity 12 of the projectile to 6 comprises a flight destabilizingdevice.

In this embodiment, at least one recess 34 a is comprised in the endwall 30 and is filled with a consumable material 36 a. There may be asecond recess 36 b filled with a non-consumable (inactive) material 36b, the two recesses for instance symmetrically arranged about thelongitudinal centre axis A. An important aspect of the arrangement ofthe consumable material and the optional non-consumable material is thatprior to ignition, the centre of gravity CG of the projectile 6 ispositioned on the longitudinal axis A. Therefore, depending on thevolume of the recess 34 a, the density of the consumable material 36 a,and the position of the centre of gravity of the consumable materialfilling the recess 34 a relative to the longitudinal axis A, the volume,position and presence of a non-consumable material may be adjusted toobtain a CG on the longitudinal axis.

In an embodiment, the consumable material may advantageously comprise orconsist of a pyrotechnically active material filling the recess 34 a andcomprising an additional layer 36 c of consumable material that isarranged around the longitudinal centre axis A in such a manner that thecentre of gravity CG of the projectile remains on its centrelongitudinal axis A even as the additional layer is thinned as it isbeing consumed. The additional layer is thus configured such that as itis consumed and thus changes in thickness, the centre of gravity of theadditional layer remains centered on the longitudinal centre axis A.

As soon as the projectile leaves the barrel, the additional layer ofconsumable pyrotechnically active material 36 c evaporates asillustrated in FIG. 10 b . After a certain time, the additional layer isconsumed as illustrated in FIG. 10 c and the consumable material 36 a inthe recess 34 a subsequently evaporates or burns. The loss of materialin the recess 34 a introduces an imbalance that displaces the centre ofgravity CG away from the projectile's longitudinal axis as shown in FIG.10 d . The moment of inertia is modified, the projectile tumbles and itsflight is aerodynamically shortened. The quantity of consumablematerial, and its rate of evaporation or combustion can be configuredsuch that tumbling occurs after a specific distance.

Other embodiments of destabilizing devices to produce flight instabilityat a specific distance may be provided. The pyrotechnical approach canrelease unevenly some material. It can also produce an explosion thatgenerates a tumbling effect. For instance, in the embodiment illustratedin FIG. 11 , a tracer type consumable material 36 a located in the aftpart of the destabilizer device 32 consumes until such time where itignites an explosive mass 47 located in the front part of thedestabilizer. The explosion detaches the destabilizer device 32 from theto projectile 6 thus producing a destabilizing effect as it leaves theprojectile.

Another embodiment of a destabilizing device to produce flightinstability at a specific distance may be externally actuated. In theembodiment illustrated in FIG. 12 a , the destabilizer device 32comprises an explosive charge 47 and an electric ignition device 41 thatis triggered by an external magnetic field of a certain minimumspecified intensity sufficient to generate an electrical current in thecoil 40 of the electric ignition device 41 for igniting the explosivecharge 47. The minimum specified or threshold intensity should begreater than the earth's magnetic field and magnetic fields generated byvarious common electrical and electronic equipment used by consumers andpersonnel that may be brought into proximity with an ammunitioncartridge, to avoid inadvertent ignition.

The electric ignition device 41 may comprise a coil 40 in which anelectric current is induced as the projectile passes through saidmagnetic field, to electrically ignite the explosive charge 47. Theexternal magnetic field may for instance be generated by a fence withelectric coils, for instance as schematically and partially representedin FIG. 12 b , positioned at the desired range limitation distance of atraining ground. The fence can be realized for instance with at leasttwo or more poles 50 of a given height on which large electric coils 51are suspended to generate the specified magnetic field.

LIST OF REFERENCED FEATURES

-   Ammunition cartridge 2    -   Casing 4        -   Base 14            -   Rim 27            -   Annular groove 29        -   Tubular sleeve 16            -   neck portion 24            -   major portion 25            -   base end 31            -   open neck end 33-   Projectile 6    -   Tip 18    -   Centre body portion 22    -   Trailing end body portion 23    -   Trailing end 20    -   Cavity 12        -   End wall 30    -   Destabilizing arrangement 32        -   Recess(es) 34, 34 a, 34 b        -   Consumable material 36 a            -   Pyrotechnically active material        -   Inactive material 36 b        -   Holder 38        -   Explosive charge 47-   Ignition device 8    -   Ignition charge 39 a, 39 b    -   Guide channel 37    -   Transmission pin 35-   Propellant charge 10    -   loose Powder, granules,    -   Solid preform        -   Leading portion 43            -   Leading end 41-   Magnetic/electromagnetic fence    -   poles 50    -   electric coils 51-   CG centre of gravity of the projectile-   CP centre of pressure of a projectile in flight-   A longitudinal centre axis of the projectile-   L length of the casing-   D maximum diameter of the casing

1.-34. (canceled)
 35. Ammunition cartridge comprising a rigid casingincluding a tubular sleeve and a base closing an end of the casing, aprojectile mounted at another end of the casing, a propellant chargecontained inside the casing, and an ignition device, the projectilecomprising a solid material body having a volume V1 extending between atip to a trailing end, wherein the casing is made of at least two partsincluding a base and a tubular sleeve that are assembled together, thetubular sleeve being made of stainless steel, and in that the projectilecomprises a cavity that extends into the body from the trailing end, avolume V2 of the cavity being between fifteen percent (15%) and fortypercent (40%) of the combined volume V1+V2 of the projectile solidmaterial and cavity: 0.15×(V1+V2)<V2<0.4×(V1+V2).
 36. Ammunitioncartridge according to claim 35, wherein the volume V2 of the cavity isat least twenty percent (20%) of the combined volume V1+V2 of theprojectile solid material and cavity: V2>0.20×(V1+V2).
 37. Ammunitioncartridge according to claim 35, wherein the volume V2 of the cavity isless than thirty percent (30%) of the combined volume V1+V2 of theprojectile solid material and cavity: V2<0.30×(V1+V2).
 38. Ammunitioncartridge according to claim 35, wherein a length (L) of the casingdivided by a maximum diameter (D) of the casing is in a range of 4.5 to7.
 39. Ammunition cartridge according to claim 35, wherein a depth ofthe cavity from the trailing end is in a range of 1 to 3 calibers. 40.Ammunition cartridge according to claim 39, wherein the depth of thecavity from the trailing end is at least 1.5 calibers.
 41. Ammunitioncartridge according to claim 39, wherein the depth of the cavity fromthe trailing end is at most 2.5 calibers.
 42. Ammunition cartridgeaccording to claim 35, wherein the propellant fills an inside of thecasing and extends at least partially into the cavity of the projectile.43. Ammunition cartridge according to claim 42, wherein the propellantis in the form of loose granules or in a solid pre-form.
 44. Ammunitioncartridge according to claim 35, wherein the projectile comprises aflight destabilizing device comprising a consumable material mounted inthe cavity and configured to deplete as the projectile flies thusoffsetting a centre of gravity (CG) of the projectile from a centrelongitudinal axis (A) of the projectile.
 45. Ammunition cartridgeaccording to claim 44, wherein the consumable material comprises orconsists of a pyrotechnically active material.
 46. Ammunition cartridgeaccording to claim 44, wherein the consumable material is mounted in arecess in an end wall of the cavity, the recess being symmetrically orasymmetrically disposed with respect to the longitudinal centre axis(A).
 47. Ammunition cartridge according to claim 46, wherein theconsumable material comprises an additional layer arranged around thelongitudinal centre axis in such a manner that the centre of gravity(CG) of the projectile remains on its centre longitudinal axis even asthe additional layer is thinned as it is being consumed.
 48. Ammunitioncartridge according to claim 35, wherein the projectile comprises aflight destabilizing device mounted in the cavity, comprising aconsumable material and an explosive charge, the consumable materialconfigured to deplete as the projectile flies until such time where itignites the explosive charge to destabilize the projectile. 49.Ammunition cartridge according to claim 35, wherein the projectilecomprises a flight destabilizing device mounted in the cavity,comprising an explosive charge, ignited by an electric ignition devicecomprising a conductive coil configured to induce an electric current inthe presence of a magnetic field to detonate said explosive charge. 50.Ammunition cartridge comprising a rigid casing including a tubularsleeve and a base closing an end of the casing, a projectile mounted atanother end of the casing, a propellant charge contained inside thecasing, and an ignition device, the projectile comprising a solidmaterial body having a volume V1 extending between a tip to a trailingend, wherein the projectile further comprises a cavity that extends intothe body from the trailing end and a flight destabilizing device mountedin the cavity.
 51. Ammunition cartridge according to claim 50, wherein avolume V2 of the cavity is at least fifteen percent (15%) of a combinedvolume V1+V2 of the projectile solid material and cavity:V2>0.15×(V1+V2).
 52. Ammunition cartridge according to claim 50,wherein, the flight destabilizing device comprises a consumable materialconfigured to deplete as the projectile flies thus offsetting a centreof gravity (CG) of the projectile from a centre longitudinal axis (A) ofthe projectile.
 53. Ammunition cartridge according to claim 52, whereinthe consumable material is mounted in a recess in an end wall of thecavity, the recess being asymmetrically disposed with respect to thelongitudinal centre axis (A).
 54. Ammunition cartridge according toclaim 53, wherein the consumable material comprises an additional layerarranged around the longitudinal centre axis in such a manner that thecentre of gravity (CG) of the projectile remains on its centrelongitudinal axis even as the additional layer is thinned as it is beingconsumed.
 55. Ammunition cartridge according to claim 50, wherein theflight destabilizing device comprises a consumable material and anexplosive charge, the consumable material configured to deplete as theprojectile flies until such time where it ignites the explosive chargeto destabilize the projectile.
 56. Ammunition cartridge according toclaim 52, wherein the consumable material comprises or consists of apyrotechnically active material.
 57. Ammunition cartridge according toclaim 50, wherein the flight destabilizing device comprises an explosivecharge, ignited by an electric ignition device comprising a conductivecoil configured to induce an electric current in the presence of amagnetic field to detonate said explosive charge.
 58. Ammunitioncartridge comprising a rigid casing including a tubular sleeve and abase (14) closing an end of the casing, a projectile mounted at anotherend of the casing, a propellant charge contained inside the casing, andan ignition device, a length of the casing divided by a maximum diameterof the casing being in a range of 4.5 to 7, the projectile comprising asolid material body having a volume V1 extending between a tip to atrailing end, wherein the projectile comprises a cavity that extendsinto the body from the trailing end, a volume V2 of the cavity beingbetween fifteen percent (15%) and forty percent (40%) of the combinedvolume V1+V2 of the projectile solid material and cavity:0.15×(V1+V2)<V2<0.4×(V1+V2), and in that a depth of the cavity from thetrailing end is in a range of 1 to 3 calibers.
 59. Ammunition cartridgeaccording to claim 58, wherein the volume V2 of the cavity is at leasttwenty percent (20%) of the combined volume V1+V2 of the projectilesolid material and cavity: V2>0.20×(V1+V2).
 60. Ammunition cartridgeaccording to claim 58, wherein the volume V2 of the cavity is less thanthirty percent (30%) of the combined volume V1+V2 of the projectilesolid material and cavity: V2<0.30×(V1+V2).
 61. Ammunition cartridgeaccording to claim 58, wherein the depth of the cavity from the trailingend is at least 1.5 calibers.
 62. Ammunition cartridge according toclaim 58, wherein the depth of the cavity from the trailing end is atmost 2.5 calibers.
 63. Ammunition cartridge according to claim 58,wherein the propellant fills an inside of the casing and extends atleast partially into the cavity of the projectile.
 64. Ammunitioncartridge according to claim 63, wherein the propellant is in the formof loose granules or in a solid pre-form.
 65. Ammunition cartridgeaccording to claim 58, wherein the casing is made of at least two partsincluding a base and a tubular sleeve that are welded together. 66.Ammunition cartridge according to claim 65, wherein the tubular sleeveis made of stainless steel.
 67. Ammunition cartridge according to claim65, wherein the tubular sleeve is made of a sheet of metal rolled into atube and welded along a seam.
 68. Ammunition cartridge according toclaim 65, wherein the tubular sleeve is made of an extruded tube ofmetal.